Sensitized ammonium nitrate explosives containing a hydrogen ion indicator



sensitive material for initiation of the explosion.

United States Patent 3,255,057 SENSITIZED AMMONIUM NITRATE EXPLGMVESCONTAINING A HYDROGEN ION INDICATOR Jerome S. Brewer, Pomona, andThurber W. Royer, Ar-

cadia, Calif., assignors to Aerojet-General tCoi-poration, Azusa,Califi, a corporation of Ohio No Drawing. Filed Oct. 10, 1963, Ser. No.315,378 3 Claims. (Cl. 1492) This application is a continuation-in-partof our copending application U.S. Serial No. 153,221, now abandoned.This invention relates to novel low cost explosives and a method fortheir manufacture. More particularly, this invention relates to novelexplosives containing a major quantity of ammonium nitrate in the formof prills and in addition nitromethane, a mixture of nitromethane withan alcohol, or an alcohol per se.

In the use of explosives, the need for safety is a problem vwhich isever present with workers in the field. Many explosives used in thefield are compounded into a finished from at the factory and shippedfrom there to the point of use. During shipment, special precautionsmust be taken. Frequently, these precautions involve limitations on therouting of the explosives and the type of carrier, etc. Further, thereare limitations as to the manner in which the explosives can be shippedand stored.

As a result of these requirements regarding shipping, storage, etc.,dynamite explosives and other sensitive boosters are quite expensive toship and store. This is reflected by a relatively high cost for theexplosive material which must be borne by the ultimate user.

In many applications in the field, it is desirable to detonate anexplosive in a small bore hole which is drilled in the rock or othermaterial to be blasted. Since ammonium nitrate-fuel oil explosivesrequire a large diama relatively large diameter hole in which todetonate and which requires a booster charge of dynamite or other Thesecond type of explosive is dynamite which is relatively expensive anddangerous to work with. This explosive is used as a booster for ammoniumnitrate-fuel oil explosives and is further used alone for blastingoperations which require the use of small diameter bore holes. Thus,present blasting operations always require the presence of largequantities of a relatively sensitive explosive such as dynamite whichmust be transported and stored as an explosive. This creates constantsafety hazards. Also, the use of two types of explosives creates storageand handling problems at the blasting site.

Many explosives are solids which are formed into a given shape in theirmanufacture. An illustration of this is the fact that dynamite generallycomes in the form of sticks. By reason of their shape it is frequentlydifficult to get the desired quantity of explosive into the bore hole.In order to meet this problem, it is common practice in the field toslit the dynamite cartridges and tamp the explosive after it is insertedinto the bore hole. This breaks down the sticks and forces the explosiveinto contact with the wall of the hole to get maximum packing density inthe hole. Tamping is a time consuming and inherently dangerous operationsince many explosives are somewhat shock sensitive.

In order to meet the above problems, it is an object of our invention toprovide a low cost multipurpose exice plosive which is as cheap asammonium nitrate-fuel oil explosives from a cost effectivenessstandpoint (amount of rock removed per cost of explosive, drilling thebore holes, etc.,) but which at the same time has properties which makeit useful for applications now performed by dynamite. It is a furtherobject of this invention to provide an explosive composed of ingredientswhich in themselves are not explosives so that they can be shipped andstored as ordinary articles of commerce. A still further object of thisinvention is to provide an explosive which does not require sensitivehigh explosive boosters, which will propagate readily in a smalldiameter bore hole, and which is free flowing so that it normally doesnot require tamping. Another object of this invention is to provide amethod for compounding an explosive which method can be readilypracticed in the field by inexperienced personnel without the use ofelaborate mixing equipment. Addtional objects will become apparent fromthe specification and claims which follow.

Our explosive composition comprises ammonium nitrate prills which arefrom about 25 to about percent saturated (if 100 percent saturated, theprills are first evacuated in vacuo) with nitromethane, a mixture ofnitromethane and a lower alcohol, or a lower alcohol. Depending upon theparticular types of ammonium nitrate prills employed, the saturationpoint ranges from about 13 to about 18 percent by weight of the totalexplosive formulation.

In addition to explosives comprising prilled ammonium nitrate andnitromethane, our invention also includes explosives comprising prilledammonium nitrate and a mixture of nitromethane with a lower alcohol. Bylower alcohol we mean an alkanol such as ethanol, methanol, andpropanol. Further, our explosives include prilled ammonium nitratesensitized with a lower alcohol. The mixture of nitromethane and a loweralcohol with prilled ammonium nitrate is preferable to our explosivescontaining only a lower alcohol with prilled ammonium nitrate. It hasbeen found that the lower alcohol-nitromethane mixture with prilledammonium nitrate provides an explosive which has a higher brisance thanprilled ammonium nitrate sensitized only with a lower alcohol. Furtherpreferred explosive compositions comprise prilled ammonium nitratesensitized with an alcohol-nitromethane mixture in which the alcohol comrises up to about 50 percent by volume of the sensitizer. A preferredalcohol for use in our explosive compositions, either alone or as thealcohol component in an alcohol-nitromethane mixture, is methanol sinceit is found that our explosives which contain this alcohol'have superiorbrisance.

The ammonium nitrate prills used in our explosives are standard items ofcommerce and are used widely as fertilizer. By prilled we mean that theammonium nitrate takes the form of spheroids as produced by dropping asuper-saturated solution of ammonium nitrate through a shot towerthrough a countercurrent flow of dry air. The individual spheres ofammonium nitrate generally range in size from about 2000 to about 5000microns in diameter. Although the particles are not completely uniformthey are generally spherical in nature and are porous with respect tonitromethane, a lower alcohol, or a mixture thereof. As purchased, theammonium nitrate prills are generally coated with an anticaking agent.The anticak-ing agent generally has little if any affect on theeffectiveness of our explosives. Thus, our invention encompassesexplosives in which either coated or uncoated prills of ammonium nitrateare used. Preferably, the ammonium nitrate prills are relatively uniformin size since we have found that such prills give a superior explosive.Nonuniform prills also give an explosive composition, however.

Patented June 7, 1966 The explosive compositions of our invention havean Oxygen balance ranging from about 25 to about +25.

Our explosives are readily mixed at the site by pouring thenitromethane, mixture of nitromethane with a lower alcohol, or a loweralcohol onto and through the prilled ammonium nitrate. Preferably,suflicient liquid sensitizer is added so as to substantially saturatethe prills. One method by which this can be readily accomplished is byadding excess liquid and pouring off the excess after the prills havesoaked for a period of a few minutes or longer. Since the quantity ofliquid absorbed by the prills and the over-all oxygen balance of theexplosive is determined by their porosity, it is not necessary for theworker to weigh the ingredients or perform any calculations informulating the explosive. Rather, all he has to do is add the liquidsensitizer until the prills are saturated and then pour off the excessliquid. In one typical case, approximately one gallon of sensitizer per50 pounds of ammonium nitrate prills gives an acceptable explosive.

Our preferred explosive compositions, therefore, are those in which theammonium nitrate prills are saturated with sensitizer, since thiscomposition makes its extremely easy for the worker to mix theingredients in the field.

In order to obtain best results, our explosive compositions should notbe allowed to stand for any prolonged period of time in contact withair. When this happens some of the liquid sensitizer can evaporate offto give a less effective explosive. In order to prevent this fromhappening, the explosive should be used within a few hours after mixingor else stored in a vapor-tight container so as to prevent evaporationof the liquid sensitizer.

Incorporated into our liquid sensitizer is a dye which colors thep-rills after the sensitizer is mixed with them. A particular dye whichwe employ is a hydrogen ion indicator or pH indicator such asdiethylaminoazobenzene or Brilliant Oil Yellow #2625, as manufactured byNational Aniline Corporation, which has .a yellow col-or. Because of thecolor of the dye, the prills take on the color of the dye when they aresaturated with the sensitizer. Sufiicient dye is employed so that thedye is about .0065 percent by weight of the total explosive composition.This informs everyone dealing with the material that the explosive isready for use and should be treated as an explosive. The dye changescolor, from yellow to red, in the presence of acid of a pH of about 4.4.After the explosive has set for some time so that a portion of thesensitizer has evaporated, the yellow dye takes on a red color on thesurface of the mixed explosive due to the ammonium nitrate. Thisindicates to people dealing with the explosive material that additonalsensitizer is needed to bring the explosive back to full strength.

In order to further illustrate our invention, there are presented thefollowing examples in which all parts and percentages are by weightunless otherwise indicated.

Example I To 84 parts of prilled ammonium nitrate were added 16 parts ofnitromethane. The explosive composition was then subjected to a numberof tests as follows:

Columnar propagation and plate dent.A 12-inch long spiral fabricatedcardboard tube having an interior diameter of one inch and a Wallthickness of one-eighth of an inch was filled with explosive. Followingthis, a No. 8 electric blasting cap was inserted in the top of theexplosive column and the material was detonated. On detonation theentire column exploded and the tube was blown apart along its entirelength.

When the above test was repeated using a two-inch inside diameter tube,the same results were obtained. In this test, the cardboard tube restedupon a one-inch thick aluminum plate which was backed up with fourinches of steel. On detonation it was found that a dent was made in theplate having a maximum depth of 0.165 inch.

Bulk density.-A small sample of the explosive was placed in a graduatedcylinder and weighed so as to determine its bulk density. The bulkdensity was found to be 0.927 gram per cc.

Underwater pressure test.-A one-pound sample of explosive was placed ina polyethylene bag having a cylindrical shape. The bag was about threeinches in diameter and had a length of approximately five inches. Afterinserting the explosive in the bag, a Du Pont E-83 detonator containing3.1 grains of Du Pont 50-25-25 ignition mix, 3 grains of lead azide, and13.5 grains of pentaerythritol tetranitrate (PETN) was placed in theapproximate center of the explosive charge and the charge was placed ina cylindrical tank having a diameter of 20 feet and filled with water.Approximately four inches from the wall of the tank was placed atransducer at a location which was approximately six feet below thewater level and about four feet from the bottom of the tank. The chargewas placed at the same depth as the transducer and approximately sixfeet from it along the major diameter of the tank. The transducer wasconnected to an oscilloscope which was calibrated to read the pressureproduced in the tank. On explosion of the charge a peak underwaterpressure of 16,700 pounds per square inch (p.s.i.) was recorded.

Impact sensitivity (Bureau of Mines) .A 20 milligram sample of explosivewas tested by the standard Bureau of Mines impact sensitivity apparatusas generally defined in US. Bureau of Mines Bulletin 346 (1931). Thetest involved dropping a two kilogram weight a measured distance againsta 20 milligram (mg) sample of explosive. The results obtained arenormally reported in terms of the minimum height in centimeters (cm.) atwhich the explosive detonated 100 percent of the time, the minimumheight at which the explosive detonated 50 percent of the time, and themaximum height at which the explosive detonated 0 percent of the time.These results are meaningless in the present case since the samplefailed to explode when the two kilogram weight was dropped from a heightof 100 cm. onto the 20 mg. sample. This was the limit of calibration ofthe test apparatus. As a comparison it was found that RDX (a standardmilitary explosive whose chemical name is cyclotrimethylenetrinitramine) detonated 100 percent of the time at a minimum height of30 cm., 50 percent of the time at a minimum height of 22 cm., and 0percent of the time at a maximum height of 18 cm.

Heat sensitivity test.A small sample of the explosive was placed in analuminum cup which was placed on a bath of Woods metal. The bath wasslowly heated to determine the temperature at which the explosive wouldburn. Readings were taken at 20 F. intervals and the bath was maintainedat a constant temperature for one minute at each of these intervals.When the bath reached a temperature of 700 F., the explosive burnedafter 6 /2 seconds.

Example I] To 84 parts of prilled ammonium nitrate were added 16 partsof a mixture comprising 30 volume percent of methanol and 70 volumepercent nitromethane. The explosive was then subjected to several testsas described in Example I. It detonated completely in the two-inchcolumnar propagation test when initiated by a Du Pont E-83 cap and madea dent in the one-inch aluminum plate which had a maximum depth of 0.182inch. The bulk density of the material was 0.891 gram per cc. and aonepound sample gave a reading of 17,000 p.s.i. in the underwaterexplosion test. Impact sensitivity was in excess of 100 cm. for 100percent and 50 percent explosion and was cm. for 0 percent explosion.

Example IIl To 84 parts of prilled ammonium nitrate were added 16 partsof a 50-50 volume mixture of nitromethane with methanol. The explosivewas found to have a bulk denplosive.

sity of 0.822 gram per cc. It detonated completely in the two-inchcolumnar propagation test and gave a plate dent having a maximum depthof 0.10 inch. Its impact sensitivity was in excess of 100 cm. for 100,50, and 0 percent detonation.

Example IV When Example IV was repeated employing isopropyl alcohol inplace of methyl alcohol, the explosive composition obtained detonatedcompletely in a steel pipe. Also, when the above examples are repeatedusing lower amounts of the liquid sensitizer, down to 25 percentsaturation of the prills, good results are obtained.

A comparative test of our explosives with one which Was superificiallysimilar involved the preparation of an explosive containing 90.3 weightpercent of prilled ammonium nitrate, 5.0 weight percent of nitromethane,and 4.7 weight percent of finely ground graphite powder. This materialwas thoroughly mixed so as to uniformly distribute the graphite powderand nitromethane within the ex- It was then tested in the underwaterexplosion test, as described in Example I, using a one-pound sample. Theexplosive failed to fire with an E-83 blasting cap as used in theprevious examples.

As set forth in the foregoing description, our explosives serve a dualfunction since they can be used in place of dynamite but yet at the sametime are cheaper from a cost effectiveness standpoint than ammoniumnitrate-fuel oil mixtures. Further, our explosives are readily formed inthe field and are composed of ingredients that are not in themselvesexplosives. Thus, the ingredients forming our explosives can be shippedand stored as ordinary articles of commerce. This results in ourexplosives being both cheap and safe to ship and store.

In addition to being cheap and safe, our explosives are quite powerful.Thus, it has been observed in field testing that our explosives are morepowerful than dynamite.

This, coupled with their free flowing properties and ability to detonatein small diameter bore holes when completely unconfined, makes themadmirably suitable for a number holes. In contrast, our explosives arerendered ineffective by coming in contact with water. This does notpresent a serious problem, however. When it is desired to use ourexplosives in applications where they come in contact with water, theycan be placed in a water repellent container such as a polyethylene bagas employed in the underwater explosion test.

Having fully defined our explosive compositions and their mode ofpreparation, we desire to be limited only within the lawful scope of theappended claims.

We claim:

1. An explosive consisting essentially of ammonium nitrate prills and aliquid sensitizer selected from the group consisting of nitromethane,and a mixture of nitromethane and a lower alkanol, said explosive havingan oxygen balance from about 25 to about H 25, and a hydrogen ionindicator.

2. An explosive composition consisting essentially of ammonium nitratepn'lls which are from about 25 to about percent saturated withnitromethane and about .0065 percent by weight diethylaminoazobenzene.

3. An explosive consisting essentially of ammonium nitrate prills and aliquid sensit-izer selected from the group consisting of nitromethane, amixture of nitromethane and a lower alkanol, and a lower alkanol, saidexplosive having an oxygen balance from about 25 to about |+25 andcontaining a hydrogen ion indicator.

References Cited by the Examiner UNITED STATES PATENTS 2,325,064 7/1943Lawrence 14947 2,721,792 10/ 1955 Hannum 149-47 3,093,522 6/ 1963Stengel et a1. 149-46 FOREIGN PATENTS 582,187 8/1959 Canada. 835,4715/1960 Great Britain.

LEON D. ROSDOL, Primary Examiner.

BENJAMIN R. PADGETT, REUBEN EPSTEIN,

Examiners. A. G. BOWEN, Assistant Examiner.

1. AN EXPLOSIVE CONSISTING ESSENTIALLY OF AMMONIUM NITRATE PRILLS AND ALIQUID SENSITIZER SELECTED FROM THE GROUP CONSISTING OF NITROMETHANE,AND A MIXTURE OF NITROMETHANE AND A LOWER ALKANOL, SAID EXPLOSIVE HAVINGAN OXYGEN BALANCE FROM ABOUT -25 TO ABOUT +25, AND A HYDROGEN IONINDICATOR.